The changing nature of love
The changing nature of love is one of the most significant themes in Another Day. Because of A's condition, in which he moves into a new body each day, being in a consistent, loving relationship with him is difficult for Rhiannon—and everyone else in his life. To try and make the relationship work, A and Rhiannon are forced to change how they view love and how they interact with each other. Rhiannon, in particular, is forced to look past A's physical changes and love him for who he is internally. Traditionally, people fall in love because of both physical reasons and intellectual reasons, not just one. In the end, this difference proves insurmountable for Rhiannon, who breaks up with A because their relationship is too difficult to continue with. Ultimately, A understands her decision but is hurt.
The mundanity of everyday life
The lives of each of the main characters in Another Day are largely mundane, just like the lives of virtually everyone in the world. At the start of the novel, Rhiannon is living day-to-day with her boyfriend, Justin. Readers very quickly see that Justin is not a good boyfriend: he is uninvolved, uncaring, and oftentimes, unkind. But Rhiannon loves him because he provides a sense of stability for her, something that she has craved for her entire life.
When A one day inhabits Justin's body, things change. Justin becomes everything he once was not. That change is welcomed by Rhiannon, whose life becomes more exciting and less mundane as a result of A. Justin's change also entices her to seek A out and start a relationship with them. Although her life still has mundane moments, she is energized by the search for A, whom she begins to love dearly. Her life was simply okay without A; it became much more exciting and better with him.
A's condition
A's condition, which forces him to take the body of a new person each day, is a central conceit in the story. It is also the biggest challenge that he and Rhiannon face. Rhiannon wants stability in her life, which is why she stays with Justin despite his disinterest in her. On the other hand, she feels deeply loved and cherished by A, who can't provide her with stability because of their condition. Because he is a new person every day, he can't possibly be a stable person in Rhiannon's life. Although A recognizes the benefits of his condition, they also want nothing more than to live a normal life and have a normal relationship with a woman they love: Rhiannon.
